Insight into the influences of thermal crosslinking on the transition from polyacrylonitrile based ultrafiltration membrane to organic solvent nanofiltration membrane

In this work, polyacrylonitrile (PAN) based organic solvent nanofiltration (OSN) membranes were prepared by combining nonsolvent-induced phase separation (NIPS) and thermal crosslinking methods. The structure and morphology changes of the PAN membrane during thermal crosslinking were investigated by Fourier transform infrared spectrometer (FTIR), X-ray photoelectron spectrometer (XPS), X-ray diffractometer (XRD) and scanning electron microscope (SEM). The thermal crosslinking reaction of PAN chains and fusion of pore structure occurred simultaneously, which were conducive to the transformation of an asymmetric PAN ultrafiltration (UF) membrane into OSN membrane. The influences of thermal crosslinking temperature and time on the structure evolutions and nanofiltration performance of PAN based crosslinked membranes were systematically investigated. The formation mechanisms of OSN membrane were discussed in terms of the evolutions of chemical structure and pore structure. The resultant thermally crosslinked membranes showed excellent thermal stability and solvent resistance in different organic solvents. Furthermore, a remarkable stability of OSN performances in long-term test was exhibited due to the formation of crosslinked ladder structure of PAN. This work showed that thermal crosslinking is an encouraging and promising method to transform UF membranes into OSN membranes.